1. Field of the Invention
The invention relates to electric motors, and in particular to electric motors having covers that cover, respectively, coil end portions protruding toward the respective axial sides of a stator and that define, respectively, a coolant chamber storing therein a coolant.
2. Description of Related Art
An electric motor is known which is provided with a stator having a plurality of stator coils circumferentially arranged at an inner periphery of a cylindrical stator core. The stator coils are each wound around one or more of teeth protruding radially inward from the inner periphery of the stator core, and the axial ends of each stator coil protrude outward from the respective axial ends of the stator, forming “coil end portions”.
Lead wires are connected to the coils, and each coil is energized with the voltage externally supplied via the lead wires, so that a current occurs at the coil. At this time, a copper loss due to the electric resistance in the coil wire (e.g., a copper wire with an insulation coating) from which the coil is formed, and this causes the coil to heat up. As the coil thus heats up and its temperature increases, the insulation of the coil degrades. In particular, in the case of multi-phase alternating current electric motors, such insulation degradation may promote electric discharges between the coil end portions of coils for different phases, between which the electric potential difference is large. In order to prevent such electric discharges, coil end portions formed as described above are cooled using a coolant, such as a cooling oil.
Japanese Patent Application Publication No. 2006-271150, which is a related-art document, describes a motor generator cooling structure. In this cooling structure, coil end portions arranged in a generally annular form and each protruding outward from an axial end face of a stator core are liquid-tightly covered by a cooling jacket filled with an externally supplied cooling oil that contacts and thereby cools the coil end portions over the entire circumference. In the cooling structure, after the coils are wound, an adaptor is attached on slot openings at the inner periphery of the stator core, so as to seal the slot openings to prevent the cooling oil, after entering each slot from the cooling jacket, from leaking to the gap between the stator and the rotor.
Further, Japanese Patent Application Publication No. 2005-323416 describes a motor generator cooling structure in which a coil is disposed in slots of a stator core, the inside of each slot is made a coolant passage by closing the opening of the slot, which opens at the inner peripheral face of the stator core, cooling jackets are provided which surround, respectively, coil end portions protruding from the front and rear ends of the stator core, respectively, and thus form annular liquid-tight spaces, coolant inlets are formed at the lower sides of the respective cooling jackets at the front and rear ends of the stator core, coolant outlets are formed at the upper sides of the respective cooling jackets, and the coolant is made to flow from the lower side to the upper side in each cooling jacket.
Further, Japanese Patent Application Publication No. 2009-177864 describes a stator having a stator core and coils wound on the stator core, wherein coil end portions of the respective coils, which axially protrude from an axial end face of the stator core, are resin-molded to be made “resin-molded coil end portions”, and this stator having the resin-molded coil end portions is characterized in that a cavity is provided in the stator core to reduce its weight. According to Japanese Patent Application Publication No. 2009-177864, in order to prevent the resin from entering the cavity when the coil end portions are resin-molded, a pair of sealing steel plates are provided on the respective axial end faces of the stator core so as to fully cover the openings of the cavity.
In both the structures described in Japanese Patent Application Publications No. 2006-271150 and No. 2005-323416, the coil end portions protruding toward the respective axial sides from the respective end faces of the stator core are shaped to be located, as viewed axially, between the inner and outer peripheral faces of the stator core, and the liquid-tight coolant passages are formed by covering the coil end portions by the cooling jackets each C-shaped in section.
However, some stator coils are formed such that no-lead-wire side coil end portions, which are coil end portions on one side, are radially large in size, protruding from an end face of the stator core radially inward. In this structure, a gap or opening is created between the inner peripheral edge of the jacket and the inner peripheral edge of the stator core. In such a case, therefore, a liquid-tight coolant chamber can not be formed by simply covering the coil end portions by a cooling jacket that is C-shaped in section. As such, electric motors having stator coils formed as described above require some measures for covering the gap or opening between the inner peripheral edge of the cooling jacket and the inner peripheral edge of the stator core if a coolant chamber needs to be formed around the coil end portions. Japanese Patent Application Publication No. 2009-177864 does not address this issue at all.